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The following SML program
exception C;
structure M :> sig exception A end =
struct
exception A = C
end;
(raise M.A) handle C => 42
returns the value 42 (according to SML/NJ and, I believe, the 1997 definition of
Standard ML).
The signature ascription appears to assert that exception A is abstract in M,
and yet we are able to raise the exception M.A and catch it as C outside the
scope of M. It makes no difference whether the signature ascription is
transparent or opaque. The equivalent OCaml program yields the same result.
Does this kind of code occur in practice?
Sam
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